The present invention relates to a rotary cutting die and, more particularly, to a method for mounting an etched rotary cutting die upon a rotating cutting cylinder.
Rotary cutting dies of this type are used as presses in the printing and packaging industries for cutting pressure sensitive labels, perforations and openings. They are used for cutting shapes in paper, plastic film and thin metal foil. Pressure sensitive labels, markers, and other similar articles formed by these cutting dies are usually made available in strips or rolls. A plurality of such labels or the like are attached to an elongated backing layer by a pressure sensitive adhesive in these strips or rolls. The pressure sensitive adhesive or gum is permanently adhered to the back of the label while the backing layer is provided with a release coating. Hence, a label having pressure sensitive adhesive separates readily from the backing layer or release layer. The user of these labels merely peels the labels or markers from the backing layer and applies the peeled-off labels or markers as required.
In order to manufacture these labels or markers on a mass production basis a strip comprising a layer of label material, a layer of pressure sensitive adhesive and a backing layer are assembled and passed under the cutting die. The cutting die may have any convenient arrangement or array of patterns thereon in accordance with the shapes desired for the labels. The labels are formed by cutting through the layer of label material adhered to the backing layer. The die also cuts through the adhesive layer beneath the layer of label material. However, the dimensions of the cutting edge, as well as the tolerance of the dimensions, are selected to prevent the die from cutting through the backing layer. In this manner a continuous strip or sheet of labels is maintained.
Prior art cutting dies suitable for preparing these label strips had the undesirable characteristic of tending to crush the label material into the backing layer or release layer, thereby weakening or destroying the latter. This occurred because the label material and backing layer are often made of paper and the edges of the cutting dies had flat lands or faces. The flat faces resulted from the fact that the cutting edges were of such a small size that mechanical techniques for forming them were not feasible, and the edges were therefore prepared by photo etching processes. The photoetching processes known in the prior art tended to produce somewhat flat cutting edges.
Accordingly, there was a need for a method for providing an improved die for cutting labels and the like in such a manner that the crushing effect and resultant weakening of the backing layer caused by the dies of the prior art could be avoided. This problem, as well as other problems of the prior art, was addressed by U.S. Pat. No. 3,850,059, issued to Pierson S. Kang on Nov. 26, 1974. Kang taught a die having a base with a raised cutting edge extending from the base. The lateral extent of the cutting edge defined a pattern for the labels or the like to be cut. The profile or cross section of the cutting edge remote from the base was rounded so that the portions of the cut layer on either side of a cut made by the cutting edge were cammed away from each other. Thus the uncut release layer beneath the cut layers was not crushed. Kang also taught a method for cutting labels or the like with this cutting die.
The die taught by Kang was a flexible die formed by a chemical etching process. The chemical etching of the flexible dies was performed primarily by the use of a photofabrication technique. In this photofabrication technique the metal forming the die was first coated on its front side with a photosensitive resist. The photosensitive resist was exposed to ultraviolet rays through a photographic transparency containing a clear image of the features of the die cutting pattern. Chemically etched flexible dies of this general type became widely used in the prior art because of their accuracy, their reproductibility and the low cost of chemically etched die production. Further contributing to the widespread use of etched dies of this type was the fact that they could be produced easily and quickly.
Flexible cutting dies formed by this type of chemical photoetching process were usually secured magnetically to magnetic cylinders or magnetic rollers. However, these magnetic cylinders were very expensive. Thus, despite the many advantages of chemically etched flexible dies, in some cases their use was limited by the cost of the magnetic cylinders required to secure and bear them during the cutting process.
In order to avoid the expense of the magnetic cylinders, chemically etched flexible dies were sometimes secured to non-magnetic cylinders using an adhesive layer between the die and the non-magnetic cylinder. However, this did not produce tolerances which were acceptable for cutting labels because of the unevenness of the adhesive layer. An unacceptable tolerance in the thickness of the adhesive layer between a cutting edge and the surface of a non-magnetic roller could cause the label to be cut to a depth insufficient to permit convenient peeling from the backing layer. Alternately, it could cause the backing layer to be cut and damaged by the cutting edge of the die.
To solve these and other problems the present invention provides a flexible cutting die and a method for securing such a flexible die to a non-magnetic blank cylinder. The cutting die formed using the method of the present invention has tolerances which are suitable for cutting pressure sensitive labels. Cutting edges for cutting the labels extend outwardly from one surface of the cutting die and spacer abutments, aligned with the cutting edges, extend outwardly from the opposing surface of the cutting die. The spacer abutments are positioned directly against the surface of the blank cylinder in order to position the opposing cutting edge with the required tolerances. The flexible die of the present invention is mounted on the blank non-magnetic cylinder by use of adhesive which is selectively applied to the back side of the die. Prior to applying the adhesive to the back side of the die, when the spacer abutments are formed, die cavities between the abutments are formed to provide confined regions wherein the adhesive may be disposed. Thus, no adhesive is disposed between the cutting edges of the die of the present invention and the surface of blank cylinder.